New FCC catalyst regeneration techniques call for the regenerator to be operated in a "standard" or complete mode of combustion. Older more established FCC catalyst regeneration systems operate in an incomplete mode of combustion. This invention is concerned with an incomplete mode of combustion in the regenerator. This type of system is defined wherein a relatively large amount of coke is left on the regenerated catalyst which is passed to an FCC regeneration zone from an FCC reaction zone. The content of CO in the regeneration zone is relatively high and usually greater than 1.0% by volume. Usually, the content of CO in these older systems range from 1-10% volume. The concentration of carbon on the regenerated catalyst is approximately 0.05 to 0.45.
In U.S. Pat. No. 4,435,282, Bertolacini et al, a system is devised for substantially complete combustion of coke deposited on an FCC molecular sieve catalyst. In the regenerator, hydrocarbon conversion catalyst particles are associated with particles of a platinum group metal which acts to promote the combustion of CO to CO.sub.2. The gaseous effluent derived from a regeneration zone operated in this type of "full combustion mode", (sometimes referred to as standard) has a low CO content and a high CO.sub.2 content.
A process for the control of NO.sub.x in the presence of a platinum-promoted complete combustion regenerator is disclosed in U.S. Pat. No. 4,290,878, issued to Blanton. Recognition is made of the fact that in a complete mode of combustion CO oxidation promoters produce an increased content of nitrogen oxide in the flue gas. These nitrogen oxides are reduced by employing a small (but stoichiometric) amount of an iridium or rhodium compound with the cracking catalyst sufficient to convert NO.sub.x to nitrogen and water.
In a similar manner, Luckenbach, U.S. Pat. No. 4,235,704, discloses a system for monitoring the oxides of nitrogen in a flue gas from a regeneration zone and thereafter adjusting the concentration of CO oxidation combustion promoter in the regeneration zone to maintain oxides of nitrogen concentration below a predetermined limit. This system, like Blanton, operates in a complete mode of combustion. It is discussed at column 7 that when the NO.sub.x sensor exceeds a predetermined limit of NO.sub.x in the flue gas, the catalyst added to the system contains a reduced quantity or no quantities of CO oxidation promoter. A disclosure is also made that if the rate of addition of the combustion promoter is not sufficient to adequately reduce NO.sub.x levels, a combustion promoter may be doped with a poison to selectively deactivate the combustion promoter relative to the cracking catalyst.
In U.S. Pat. No. 4,744,968 this inventor participated in an invention to reduce the quantity of ammonia in a regeneration zone (or a regenerator off-gas) by the addition of NO.sub.x either to the regenerator per se or to a flue gas exiting from the regenerator. Another invention directed to the reduction of ammonia in a regenerator was the development of the addition of a noble metal dispersed on an inorganic support wherein the noble metal catalyst possessed a size of from 10 to 40 microns. This was the essence of the invention in U.S. Pat. No. 4,755,282.
These patentees have failed to appreciate a system whereby NO.sub.x is reduced by control of ammonia in an incomplete combustion regenerator via increase in the quantity of combustion promoter in the regeneration zone. In fact, both Luckenbach and Blanton teach that under complete combustion conditions the addition of excess oxidation promoter result in an increase in NO.sub.x content.